Skip to content

Reservoir Quality and Distribution of the Basal Toolachee Formation in the Durham Downs Region, Cooper Basin, South West Queensland

James W. Nankivell
Bachelor of Science (Petroleum Geology & Geophysics) 2013
Australian School of Petroleum
The University of Adelaide


The study of the basal Toolachee reservoir sequence in the Durham Downs region of the Cooper Basin in south west Queensland, Australia, was conducted to integrate recently acquired well data from the successful Durham Downs 5 well into the existing regional dataset. The dataset was examined using a series of investigative analytical techniques that were used to provide information at a range of scales. Initially, the study used broad scale techniques such as 2D seismic analysis and regional stratigraphic correlations to confirm the presence, position and distribution of the basal Toolachee reservoir sequence. Detailed core, thin section, SEM and PERC analytical techniques were then used to examine the intricate properties of the basal Toolachee reservoir. The results of the techniques undertaken during this study have been used to identify the controls that have influenced reservoir development and distribution of the basal Toolachee reservoir sequence that was encountered in Durham Downs 5.

Regional seismic analysis and lithostratigraphic correlations have identified the distribution of the Toolachee Formation across the area. Results of the regional studies identify that the reservoir sequence encountered in Durham Downs 5 is part of the basal Toolachee sequence that directly overlies the major regional unconformity in the area. Core analysis has identified that the basal Toolachee reservoir sand is best developed in Durham Downs 5 and consists of a series of stacked channel units. Sand of this quality has not been identified in any of the other cores in the Durham Downs area. The high permeabilities in the stacked channel sequence are interpreted to be the result of excellent secondary porosity development.

In complex areas such as Durham Downs, other methods need to be used to predict where the better reservoir sand is likely to be situated. One way this can be achieved is by using PERC analysis to identify regional sand quality trends. The PERC analysis conducted during this project when used in conjunction with other data, has the potential to highlight areas where future exploration efforts should be focused.

Australian School of Petroleum



T: +61 8 8313 8000
F: +61 8 8313 8030